The specific research objectives and plan in this work are: 1. To determine, by genetic manipulation, the important control elements that regulate SV40 gene expression. 2. To construct, by biochemical methods, a series of well defined non-viable deletion mutants in the putative control segments of an SV40-hybrid virus; SV40-beta globin. 3. To determine the effects of the constructed deletion mutants on the expression and processing of the beta globin sequences thus circumventing the difficulties of studying non-viable mutants and taking advantage of the extensive molecular knowledge of the globin gene. 4. To follow transcriptional changes during defective SV40 evolution and during the establishment of persistent SV40 infections. 5. To characterize the alterations in SV40 "defectives" that abnormally "splice" RNA.